Inspection and repair of blades on wind turbines are associated with high financial costs, on the one hand in the form of loss of earnings while the turbine is out of operation and, on the other, by the work itself. It is an option to dismount the damaged blade and mount another one straightaway, whereby the operation of the turbine can swiftly be resumed. However, the costs involved in such course of action are considerable, on the one hand for the new blade, on the other for crane, ship or helicopter for the mounting, to which is to be added that the replacement is possible only in calm weather conditions, which may pose a problem in particular in case of off-shore turbines.
Servicing and repair of the blade may in most instances, unless the damage is to extensive, also be performed while the blade is mounted on the wind turbine. This is usually done by means of various kinds of working platforms taken along the blade while it is in its vertical position down along the tower. The platforms are conveyed by cranes from heavy vehicles or ship and are connected to tower or hub. Alternatively, inspection can be performed by the crew rappelling down the blade from the nacelle which, however, is difficult to accomplish in adequately safe conditions. The use of both mobile cranes and ships with cranes is, however, as mentioned above, associated with high costs. Add to this that the area of repair is comparatively limited on a vertically situated blade, and that not all repairs can be suitably performed on a vertical face.
From WO 2004/070203 it is known to mount a blade on a wind turbine while the blade is kept in a horizontal position. In order to enable lifting of the blade, it is provided with one or two bores extending all the way through the blade shell, to which holes the lifting gear is mounted. The holes are closed following mounting to prevent ingress of water and soil and so as not to destroy the aerodynamic properties of the blade, and therefore they are not suitable for use in case of servicing and ordinary maintenance of the blade; they are useful only when the blade is being mounted. It is also a further considerable drawback of the method that holes through the entire blade shell will inevitably considerably reduce the strength and rigidity of the laminate and hence of the blade in a considerable area around the holes. Only very few holes with large mutual distances are therefore just barely acceptable, meaning that such holes are not applicable in servicing scenarios.